Debugger: initialise SavedAddress.address with 0 instead of NULL

[nekopsykose]

Description of Changes

Uses an int 0 instead of NULL as the initialiser for the default address

Rationale behind Changes

In c++11 and higher it's valid for NULL to be nullptr_t instead of just a 0 or ((void *)0) (see https://en.cppreference.com/w/cpp/types/NULL , though the only platform that i know of that actually does this by default via their stddef.h is musl libc). When that's the case:

../pcsx2-qt/Debugger/Models/SavedAddressesModel.cpp:122:42: error: cannot initialize a member subobject of type 'u32' (aka 'unsigned int') with an rvalue of type 'std::nullptr_t'
  122 |         const SavedAddress defaultNewAddress = {NULL, "Name", "Description"};
      |                                                 ^~~~

since the intent is a default for u32, a 0 works all the time.

Suggested Testing Steps

None needed.

[stenzek]

Was about to fix this tonight.